<!DOCTYPE HTML>
<html>
<head>
<title>Testcase</title>

<style>

body {
  margin: 0px;
  padding: 0px;
}

#inner {
  width: 100px;
  height: 100px;
  background: linear-gradient(red, blue) no-repeat;
  background-position: -50px -50px;
  background-size: 800px 800px;
}

#outer {
  margin: 50px 50px 0;
  width: 100px;
  height: 200px;
  clip-path: url(#path);
  position: fixed;
}

</style>
</head>
<body>
<div id="outer">
  <div id="inner"></div>
</div>

<svg height="0">
  <defs>
    <clipPath id="path" clipPathUnits="objectBoundingBox">
      <polygon points="0.25,0.25 0.25,0.75 0.75,0.75 0.75,0.25"/>
    </clipPath>
  </defs>
</svg>
</body>
</html>
